At the end of Route 4 you're presented with a choice. Either continue north and on to Nimbasa City, or head west and check out Desert Resort. It's not a compulsory diversion, but since there are a ton of items to be found...

Your first job when you enter the Desert Resort is to talk to the nurse a little ways north of the entrance. You'll be challenge to a quick fight.

Nurse Mariah

Cleffa, level 22

Reward: 880 Pokedollars

Nurses in Pokémon Black 2 and White 2 serve the exact same role as doctors: they will restore the health of the pokémon on your team. Mariah is thus fantastic for searching Desert Resort, as you may often need to heal - the Resort's constant sandstorm status will slowly whittle down your pokémon.

(The rest of this walkthrough will assume a north-to-west-to south-to-west-to-north-and-so-forth search pattern. If you want to wander around in your own pattern you will run into people at different times.)

To your immediate north, patrolling a small stretch of sand, is a trainer.

Ranger Adja

Magby, level 23

Reward: 1380 Pokedollars, Rawst Berry

To the east of the ranger is a Yellow Shard against a canyon wall. Grab it, then talk to the suited man in the nearby pit. He'll give you Soft Sand for your ground-type pokémon, which will come in very handy for the next gym. Further north you'll find a deep sand pit; hidden near the top of it is a Super Repel.

Head west a full screen to find a Heart Scale. To the immediate south is a set of stairs, and near them a trainer. Challenge him first.

Psychic Tommy

Woobat, level 22

Yamask, level 22

Reward: 704 Pokedollars

Pull out your Dowsing Machine to find a Ground Gem near the edge of this small hill, then go down the stairs. You're now in the Relic Castle, an area you can't fully explore at this point. Head west, slowly skirting the edge of the sand pit (if you run you'll slip in) and fight the trainer near the next set of stairs.

Psychic Perry

Sigilyph, level 23

Reward: 736 Pokedollars

Down the stairs from the first psychic you'll run into another one.

Psychic Dua

Gothita, level 23

Reward: 726 Pokedollars

Behind the trainer you'll find TM39 Rock Tomb. There's a great deal more to Relic Castle, but you can't get to it - not from here, anyway. You'll be back here later. Head back to the Desert Resort and carry on southbound.

On a nearby hill you'll see a trainer moving around in a circle. Stop her and battle here.

Backpacker Clara

Sandshrew, level 22

Reward: 528 Pokedollars

After beating the backpacker, check the spot she was so dutifully circling. You'll find a Blue Shard. Grab it, then go down the hill to the east and check through the sand. Near the center, hidden in the sand, is a Star Piece. Continue south to find another trainer.

Ranger Jaden

Darumaka, level 23

Reward: 1380 Pokedollars, Rawst Berry

In a pit near the ranger is a Stardust. Grab it, considering backtracking a little ways east to heal, then continue west. You'll find a sand pit in the shape of a plus sign; to the south of this is a Green Shard. Head north once you have it and, soon, you'll see a Blue Shard in a small pit. Further north yet is another trainer.

Backpacker Walt

Sandile, level 22

Reward: 528 Pokedollars

Walt, like the previous backpacker, was also circling something: a Red Shard. Snag it, then carry on north until you reach the edge of the area. Up here you'll find a trainer circling a patch of rubble.

Psychic Future

Munna, level 23

Reward: 736 Pokedollars

On a small rise up here is a Nugget. The rubble used to be an entrance to Relic Castle; you can't go through there anymore. Oh well. Head back south.

After a big patch of deep sand you'll come across a backpacker by some rocks. Grab the item near him - a Red Shard - then get into a fight with the man.

Backpacker Sam

Dwebble, level 22

Reward: 528 Pokedollars

Go south from the backpacker and enter the small niche between the rock walls. Inside you'll be challenged by another backpacker.

Backpacker Tami

Drillbur, level 22

Reward: 528 Pokedollars

Run south from here and you'll find a series of narrow passages between the rocks. Check to the southeast of the entrance to find a Fire Stone in a corner using your Dowsing Machine, then check to the west of the stone for a Max Ether.

That's it! You've covered the entirety of Desert Resort. You can now head back to Route 4 and carry on north to Nimbasa City. Hopefully you got yourself a good ground-type pokémon, as the gym leader in your near future loves shocking her opponents.